The long-range objective of this proposal is to characterize the functional alterations of the cerebral microcirculation associated with acute or sustained experimental hypertension. We propose a systematic study which will examine important aspects of the responsiveness of the microcirculation of the brain to physiological stimuli, of alterations in blood-brain barrier permeability and of the changes in the metabolism of the arteriolar smooth muscle. These abnormalities will be studied sequentially in the course of acute or sustained experimental hypertension and will be related to the morphological alterations seen in these vessels. The experiments will utilize direct microscopic observation of the vessels on the surface of the brain viewed through chonically implanted cranial windows, and new methods for measuring the permeability of the blood-brain barrier. Oxygen consumption of the arterioles studied will be measured with the Cartesian diver.